[services] Clean up run_integration_tests.sh using ShellCheck

Summary: Related Linear issue here. This is part of a set of diffs that will allow ShellCheck to be added to the CI. See inline comments for specific details of the ShellCheck error/warning output.

Test Plan:
I went to @karol's initial diff where this code was introduced (D4216) and ran the Test Plan he noted there. Specifically, I ran:

cd services
yarn run-integration-tests backup
yarn run-integration-tests blob
yarn run-integration-tests all

However, all these failed.

I also checked out a new branch off origin/master and the same commands failed in the same fashion. So it doesn't have to do with the code in this diff, this diff is purely for ShellCheck purposes. But we should definitely figure out what's going wrong there.

Reviewers: atul, jon, tomek, karol

Reviewed By: jon, karol

Subscribers: ashoat, adrian, karol

Differential Revision: https://phab.comm.dev/D4724